Vacuum pump

ABSTRACT

A vapor vacuum pump including a housing enclosing a cooled baffle and vapor jet assembly. A cooled multipart trap is positioned within the housing in the gas flow path. One portion of the trap is secured to and extends through the side wall of the housing to act as a heat sink while the other portion extends through the top of the housing and is thermally connected to the heat sink portion of the trap.

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1/1974 Long..... 11 Claims, 2 Drawing Figures Attorney, Agent, or Firm-Dennison, Dennison, Townshend & Meserole part trap is positioned within the housing in the gas flow path. One portion of the trap is secured to and extends through the side wall. of the housing to act as a heat sink while the other portion extends through the top of the housing and is thermally connected to the heat sink portion of the trap.

Primary Examiner-William .ll. Wye

Limited, Crawley, England [22] Filed: Mar. 8, 1974 [21] Appl. No.: 449,551

[30] Foreign Application Priority Data Mar. 8, 1973 United Kingdom...........,...

[52] U.S. Cl.

[Sl] int. [58] Field of [56] References Cited UNITED STATES PATENTS PATENTEDSEP 2W 3, 902,330

SHEET 1 OF 2 PATENTEDSEP zi vs 3, 902 330 sum 2 u; 2

VACUUM PUMP This invention relates to a vacuum pump, and particularly to a vapour vacuum pump.

The present invention aims at improving the vapourtrapping efficiency by including a refrigerated trap so that incident vapour molecules become condensed or frozen on the trapping surfaces.

Accordingly the present invention provides a vapour vacuum pump as claimed in the appended claims.

The present invention will now be described by way of example with reference to the accompanying drawings, in which:-

FIG. 1 is a side view, part in section and part in elevation, of one form of vapour vaccuum pump of the present invention, and

FIG. 2 is a fragmentary view of part of the pump shown in FIG. 1, with an alternative form of heat sink.

Some of the numbered references shown in the draw ings are to components of the vapour vacuum pump described in our US. Pat. No. 3,801,225 which is incorporated herein by reference. The description and function of many of these components are as described in US. Pat. No. 3,801,225 and therefore will not be described further in this specification, which will be limited to components relevant to the present invention.

The housing 2 of the vapour vacuum pump of the present invention is belled-out in the region of the upper nozzle 42 of the vapour jet assembly. This leaves a gas flow passage of sufficiently-large cross-sectional area between the adjacent part of the housing 2 and the water-cooled baffle member 10, of which most is positioned above the vapour jet assembly but which includes a water-cooled skirt 54 extending below the upper vapour nozzle 42 to function as a cold cap.

As shown in FIG. I, the belled-out portion of the housing has a cylindrical part 70 which is cooled by means of wrapped tubes 8 through which is passed a flow of cold water. An annular seat or flange 72 is secured to the outer surface of the cylindrical wall 70 in a vacuum-tight manner. such as by being welded or brazed thereto. The seat 72 defines a cylindrical opening into the interior of housing 2,'and also provides a substantially planar, annular seat for a thermal stand off member 74 which is able to be secured to seat 72 by several screws 76.

The stand-off member 74 is preferably of stainless steel or like material having a low thermal conductivity and yet sufficient mechanical strength to support a heat sink member 78 intended to be inserted into the interior of housing 2. The gap between member 74 and insert 78 is evacuated when the pump is in use, so that the insert 78 is vacuum insulated thermally from housing 2.

The insert 78 is adapted to be refrigerated to a suita bly-low temperature by any convenient means. The means shown in the drawing, but only be way of example, is to mount on the outer end of insert 78 a device 80 which is adapted to cool the outer end of the insert by using the Peltier effect, which is a phenomenon whereby heat is liberated or absorbed at ajunction between dissimilar metals when electric current is passed across the junction. The current is introduced to device 80 by electrical leads (not shown) and insert 78 is in thermal contact with that junction which absorbs heat when current is passed through it. The junction which liberates heat is cooled as by water or air introduced through conduits 82. The rate of absorption of heat by the cold junction is designed to be sufficiently great for the trapping surfaces (to be described below in greater detail) to be cooled to a sufficientlylow temperature below that which the water-cooled baffles reach in use.

FIG. 2 shows in greater detail than in FIG. 1 an alternative form of Peltier-effect device, Parts already shown in FIG. 1 have been given the same references.

The seat 72 has secured directly to it a housing 96 containing a Peltier-effect element 98 having its hot junction in contact with a wall 100, and its cold junction in contact with the outer end of heat sink member 78. The electrical conductors to element 98 have been omitted from the drawing for clarity. Mechanical compression forces on the contacting surfaces are applied by a strained frusto'conical spring 102. The wall 100 is cooled by water introduced and exhausted through conduits 82.

The heat sink 78 is supported by a stand-off 74 which is introverted compared with that shown in FIG. I. The hollow cylindrical space between stand-off 74 and heat sink 78 is preferably filled with a thermal insulant, such as cellulosic fibres. This is to insulate the heat sink 78 thermally from the water-cooled casing 2 of the pump, which casing is relatively warm compared with the temperature attained by heat sink 78 in use.

Although a Peltier device has been described as providing the necessary degree of refrigeration, cooling of the insert 78 can be achieved by any other convenient means. For example, the outer end of a modified insert could be arranged to dip into a body of liquid nitrogen or other cryogenic liquid; it could be provided with internal passages along which could flow a suitable refrigerant liquid, such as that sold under the trade mark FREON, or the insert 78 could take the form of a thermodynamic engine adapted to remove heat.

The characterising feature of the present invention is that the refrigerated trap is in the form of at least two separable portions. The insert 78 functions as the main part of one portion, while the other portion 84 provides the trapping surfaces themselves.

Portion 84 comprises basically a dish 86 supporting an array of three frusto-conical members 88, these members being supported by means of stands 90 having slots into which the members 88 fit, the stands 90 being intended to be positioned on the base of dish 86. The stands 90 (of which only one is shown) are in good thermal contact with both the members 88 and the dish 86, being normally secured thereto by being soldered or brazed.

The dish 86 and the members 88 have the distinguishing characteristic that they are each able to be passed through the part of the isolation valve 12 when the valve plate 64 of the valve is removed therefrom. When in the assembled position shown in the drawing the dish 86 and members 88 cooperate to form an optical trap which prevents there being a line-of-sight from the interior of the upper part of the vapour pump housing to any part of the isolation valve 12 or adjacent surface. Because vapour molecules tend to travel in straight lines for long distances under the high vacuum attained in the interior of the vapour pump housing. satisfying the optical trap criterion ensures that no such vapour molecule is able to impinge directly on an unrefrigerated surface upstream of the trap, and the degree of cooling of the dish 86 and members 88 is such that vapour molecules incident on the dish or members become condensed or frozen thereto and are not able to impinge subsequently on any warmer surface from which the molecules might be reevaporated and enter the equipment being evacuated.

For the refrigerated trap to work as intended. it is necessary for all the components thereof to be in good heat transfer relationship with insert 78. This is ensured by fastening the dish 86 securely to a flat surface of insert 78. This is done by means of a metal strip 92 through which screws 94 pass into tapped holes (not shown) in insert 78. Access to the screws is of course provided through the part of the isolation valve 12. As mentioned above, it is preferred for the stands 90 to be brazed or otherwise secured to the dish 86 so that heat is able to flow freely from all the members 88 to the dish 86, and thence to insert 78.

When the trap is to be dismantled, the mounting assembly is reversed. First the isolation valve 12 has the valve plate 64 removed and then the screws 94 are unscrewed until all the trapping surfaces can be removed as a unit through the opening so formed, together with the strip 92 and screw 94. When this has been done the screws 76 can be removed to permit insert 78 to be withdrawn from the interior of the housing 2, for repair or replacement, but mainly to give access to pump components lower down inside the pump housing 2. It will be noted that all these components are dimensioned so as to enable them to be withdrawn through the port of the isolation valve.

It will thus be seen that the present invention provides an improved vapour vacuum pump in which the vapour-trapping efficiency is increased by providing refrigerated surfaces so arranged that there is a high probability that any vapour molecules migrating towards the pump mouth will collide with them and thereby become immobilised.

I claim:

1. A vapour vacuum pump having a housing internally of which there is a water-cooled baffle and a vapourjet assembly; a trap positioned in the gas flow path upstream of the baffle, and adapted to be cooled, the trap being in two separate portions, of which one portion is insertable through the wall of the housing. and is able to be secured thereto. the said one portion having heat extraction means so that it acts as a heat sink, and of which the other portion functions as a trap, being insertable through the top of the housing and being able to be connected thermally to the said heat sink portion, said heat extraction means including a mechanical support for the said trap portion within the housing. the support extending through the housing wall to the exterior thereof and carrying means for cooling on its outer end outward of the housing for cooling the support to a temperature substantially below room temperature.

2. A vapour vacuum pump as claimed in claim I, in which the said cooling means utilises a Peltier-effect device.

3. A vapour vacuum pump as claimed in claim 2, in which means are provided for removing heat liberated during operation of Peltier-effect device.

4. A vapour vacuum pump having a housing internally of which there is a water-cooled baffle and a vapourjet assembly; a trap positioned in the gas flow path upstream of the baffle, and adapted to be cooled, the trap being in two separate portions, of which one portion is insertable through the wall of the housing, and is able to be secured thereto, the said one portion having heat extraction means so that it acts as a heat sink. and of which the other portion functions as a trap, being insertable through the top of the housing and being able to be connected thermally to the said heat sink portion. said heat extraction means including a mechanical support for the said trap portion, the support also carrying means for cooling its outer end to a temperature substantially below room temperature, the support being mechanically secured to the pump housing by means of a thermal stand-off.

5. A vapour vacuum pump as claimed in claim 4, in which the thermal stand-off takes the form of a thinwalled tube extending in parallel with and spaced radially from, the support, the tube being connected at one end to the support in a vacuum-tight manner. and at the other end to a member adapted to be detachably connected to the pump housing.

6. A vapour vacuum pump as claimed in claim 5, in which the thermal stand-off projects externally from the pump housing, and in which the space between the said support and the thin-walled tube is in communication with the interior of the pump housing so that it is evacuated when the pump is in operation.

7. A vapour vacuum pump as claimed in claim 5, in which the thermal stand-off projects internally into the interior of the pump housing, and in which the space between the support and the thin-walled tube contains thermal insulation material.

8. A vapour vacuum pump having a housing internally of which there is a water-cooled baffle and a vapourjet assembly; a trap positioned in the gas flow path upstream of the baffle, and adapted to be cooled, the trap being in two separate portions, of which one portion is insertable through the Wall of the housing, and is able to be secured thereto. the said one portion having heat extraction means so that it acts a heat sink, and of which the other portion functions as a trap, being insertable through the top of the housing and being able to be connected thermally to the said heat sink portion, said trap portion taking the form of a dish adapted to be detachably connected to the said one portion and to support an array of vertically-spaced trapping members in thermal contact with the dish.

9. A vapour vacuum pump as claimed in claim 8, in which the trapping members are supported by means of stands projecting upwardly from the dish, the stands being slotted, with the trapping members fitting into the slots.

10. A vapour vacuum pump as claimed in claim 8 in which each trapping member is in the form of a frustoconical member, the dish and the trapping members cooperating to form an optical trap.

11. A vapour vacuum pump as claimed in claim 9 in which the dish. the slotted stands and the trapping members are firmly secured to each other by brazing material. 

1. A vapour vacuum pump having a housing internally of which there is a water-cooled baffle and a vapour jet assembly; a trap positioned in the gas flow path upstream of the baffle, and adapted to be cooled, the trap being in two separate portions, of which one portion is insertable through the wall of the housing, and is able to be secured thereto, the said one portion having heat extraction means so that it acts as a heat sink, and of which the other portion functions as a trap, being insertable through the top of the housing and being able to be connected thermally to the said heat sink portion, said heat extraction means including a mechanical support for the said trap portion within the housing, the support extending through the housing wall to the exterior thereof and carrying means for cooling on its outer end outward of the housing for cooling the support to a temperature substantially below room temperature.
 2. A vapour vacuum pump as claimed in claim 1, in which the said cooling means utilises a Peltier-effect device.
 3. A vapour vacuum pump as claimed in claim 2, in which means are provided for removing heat liberated during operation of Peltier-effect device.
 4. A vapour vacuum pump having a housing internally of which there is a water-cooled baffle and a vapour jet assembly; a trap positioned in the gas flow path upstream of the baffle, and adapted to be cooled, the trap being in two separate portions, of which one portion is insertable through the wall of the housing, and is able to be secured thereto, the said one portion having heat extraction means so that it acts as a heat sink, and of which the other portion functions as a trap, being insertable through the top of the housing and being able to be connected thermally to the said heat sink portion, said heat extraction means including a mechanical support for the said trap portion, the support also carrying means for cooling its outer end to a temperature substantially below room temperature, the support being mechanically secured to the pump housing by means of a thermal stand-off.
 5. A vapour vacuum pump as claimed in claim 4, in which the thermal stand-off takes the form of a thin-walled tube extendinG in parallel with and spaced radially from, the support, the tube being connected at one end to the support in a vacuum-tight manner, and at the other end to a member adapted to be detachably connected to the pump housing.
 6. A vapour vacuum pump as claimed in claim 5, in which the thermal stand-off projects externally from the pump housing, and in which the space between the said support and the thin-walled tube is in communication with the interior of the pump housing so that it is evacuated when the pump is in operation.
 7. A vapour vacuum pump as claimed in claim 5, in which the thermal stand-off projects internally into the interior of the pump housing, and in which the space between the support and the thin-walled tube contains thermal insulation material.
 8. A vapour vacuum pump having a housing internally of which there is a water-cooled baffle and a vapour jet assembly; a trap positioned in the gas flow path upstream of the baffle, and adapted to be cooled, the trap being in two separate portions, of which one portion is insertable through the wall of the housing, and is able to be secured thereto, the said one portion having heat extraction means so that it acts as a heat sink, and of which the other portion functions as a trap, being insertable through the top of the housing and being able to be connected thermally to the said heat sink portion, said trap portion taking the form of a dish adapted to be detachably connected to the said one portion and to support an array of vertically-spaced trapping members in thermal contact with the dish.
 9. A vapour vacuum pump as claimed in claim 8, in which the trapping members are supported by means of stands projecting upwardly from the dish, the stands being slotted, with the trapping members fitting into the slots.
 10. A vapour vacuum pump as claimed in claim 8 in which each trapping member is in the form of a frusto-conical member, the dish and the trapping members cooperating to form an optical trap.
 11. A vapour vacuum pump as claimed in claim 9 in which the dish, the slotted stands and the trapping members are firmly secured to each other by brazing material. 